The general objective in this research is to apply the methods and point of view of physical chemistry to the study of reactions of biological importance. Emphasis is placed on thermodynamic, especially calorimetric, and to a lesser extent kinetic methods and interpretations. Two broad areas are of particular interest to us: (a) the mechanism of enzyme catalyses and other biochemical reactions, and (b) the thermodynamics of biopolymeric systems. Our activities in these areas can be illustrated by examples taken from work currently in progress. The effects of various additives and conditions on phase transition behavior of lipid bilayers is being studied, primarily by high sensitivity differential scanning calorimetry (DSC). Lipids from both natural and synthetic sources are employed. New DSC observations on the polymerization of the coat protein of tobacco mosaic virus raise intriguing problems in connection with the mechanism of this process. It is known from X-ray studies that the binding of glucose to yeast hexokinase causes a substantial conformational change in the protein. Despite this, the process nevertheless leads to a very small enthalpy change. Studies on this system are being continued to evaluate the heat capacity change in the process.